Constraints on enhanced extinction resulting from extinction treatment in the presence of an added excitor

Three Pavlovian fear conditioning experiments with rats as subjects explored the effect of extinction in the presence of a concurrent excitor. Our aim was to explore this particular treatment, documented in previous studies to deepen extinction, with novel control groups to shed light on the processes involved in extinction. Relative to subjects extinguished on the target CS alone, Experiments 1 and 2 found across a range of parameters that any appreciable effect of facilitated extinction due to the concurrent excitor was submerged by generalization decrement going from extinction to testing. In Experiment 3 we used different durations for the target and concurrent stimuli in order to discourage configuring and an ABC renewal design to increase sensitivity, and observed diminished renewal resulting from extinction in the presence of a second excitor. Our findings suggest that there are distinct limits to the observation of enhanced extinction in the presence of an excitor and identifies some of the sources of these limitations.     

Reduced blocking as a result of increasing the number of blocking cues

Weak behavioral control (blocking) occurs when a target stimulus (X) is paired with an outcome in the presence of a well-established signal for the outcome (i.e., a blocking stimulus). Conventional Pavlovian conditioning theories explain this effect by asserting that a discrepancy between expected and experienced outcomes is necessary for learning about X and that no such discrepancy exists in blocking situations. These theories anticipate that the effect of additional well-established signals for the unconditioned stimulus (US) should be additive. In two conditioned barpress suppression experiments using rats as subjects, the opposite result was observed. Experiment 1 provided evidence that blocking was reduced when two blocking stimuli were present during X-US pairings relative to when one blocking stimulus was present. Experiment 2 elaborated on the mechanisms underlying the observations in Experiment 1, while explaining the discrepancy between the results of Experiment 1 and prior reports of the additivity of blocking stimuli. nt]mis|The research was supported by National Institute of Mental Health Grant 33881.     

A comparator view of Pavlovian and differential inhibition

In 3 experiments using rats as subjects, the authors varied trial spacing to investigate the conditions under which Pavlovian and differential inhibition are observed. Experiment 1 compared Pavlovian and differential inhibition with spaced training trials. Spaced trials resulted in only the Pavlovian inhibitor passing both summation and retardation tests. Conversely, Experiment 2 compared these 2 types of inhibition with massed training trials. This training resulted in only the differential inhibitor passing both tests for conditioned inhibition. Finally, in Experiment 3 all subjects experienced Pavlovian inhibition training with massed trials. Although this training by itself did not result in behavior indicative of inhibition, subjects that also experienced posttraining extinction of the training context did pass both tests for inhibition. Overall, these results are anticipated by the extended comparator hypothesis (Denniston, Savastano, & Miller, 2001) but are problematic for most contemporary associative learning theories.     

Counteraction between two kinds of conditioned inhibition training

In a Pavlovian fear-conditioning preparation, we investigated the effects of combining Pavlovian and explicitly unpaired inhibition treatments. A summation test for inhibition suggested a strong tendency toward unpaired inhibition when that treatment was administered alone and found robust Pavlovian inhibition when that treatment was administered alone, but detected little behavior indicative of inhibition in subjects that experienced both treatments during training. The retardation test showed reliable unpaired and Pavlovian inhibition when these treatments were administered alone but no indication of inhibition in subjects that experienced both treatments. These counterintuitive results suggest that in some circumstances the effects of two inhibitory treatments are not additive but rather counteractive. The present results provide some information about the nature of conditioned inhibition and, more generally, cue interaction.     

On the generality and limits of abstraction in rats and humans

In this review, we address the question, central to cognition, of whether nonhuman animals such as rats are capable of extracting and extending information from a given learning situation to a new learning situation without generalizing through a physical dimension of the stimuli. This capacity underlies abstraction, which is a hallmark of human cognition and necessary for complex information processing such as language acquisition. We selectively review recent experiments with rats in which systematic changes in information processing of new stimuli are observed after training with different stimuli. These results strongly suggest that this capacity is present in rats. We also review two articles in which clear limitations to this capacity are detected. We conclude that, within specified limits, rats are capable of using prior experience when faced with a learning situation that involves new stimuli. We interpret this ability as a rudimentary form of abstraction. In the face of these provocative results, new theories of learning should be designed to account for these findings.     

Counteraction between overshadowing and degraded contingency treatments: support for the extended comparator hypothesis

Four experiments using rats in a Pavlovian lick-suppression preparation investigated the effects of combining 2 treatments known for their response-decrementing effects, namely, overshadowing and degraded contingency. Contrary to most contemporary learning theories, the extended comparator hypothesis predicts that these 2 treatments will counteract each other, and therefore, less of a decrement in conditioned responding should be observed than with either treatment alone. Experiments 1 and 2 confirmed this prediction in first-order conditioning and sensory preconditioning preparations, respectively. Experiment 3 demonstrated that posttraining extinction of the training context resulted in a recovery from degraded contingency and reversed the counteractive effect on overshadowing. Finally, Experiment 4 demonstrated that posttraining extinction of the overshadowing stimulus resulted in recovery from simple overshadowing and also reversed the counteractive effect on degraded contingency. These results are consistent with the extended comparator hypothesis but not traditional or recent acquisition-focused models.